Household appliances such as mixers, blenders and food processors typically comprise a housing, a stirring shaft and a mixing bowl. The housing usually includes a head, a stem and a base. Generally, the stirring mechanisms can be divided into two types,
The first type is the top-mixing type, which has the motor and coupling mechanism within the head of the housing of the appliance, such as in bench-top cake mixers. Typically, the head is rotatable, such that one or two stirring shafts have to be manually attached to the coupling mechanism, followed by the placement of the mixing bowl on the base of the housing. The head of the housing is then rotated such that the stirring shaft is rotated into the mixing bowl and points towards the bottom of the mixing bowl. In a variation of this top-mixing design, the head is not rotatable, and the shaft has to be attached manually by the operator having access between the mixing bowl and the head of the housing. This non-rotatable design is often found in industrial scale mixers, which have housing heads containing motors which are too large, heavy or bulky to be conveniently rotated. The advantage of having a top-mixing design is that the base of the housing can contain additional useful function, such as heating or rotating elements. The disadvantage of this design is that a relatively large space must be left between the mouth of the mixing bowl and the head of the housing. In the rotatable head design, this is necessary to give sufficient room for the shaft to be lowered down into the bowl after being attached. In the non-rotatable design, this space is necessary for the operator to access the coupling point with the stirring shaft inside the bowl. As a result, the mixing bowls are often wide and shallow, and cannot be provided with a lid. Because of the need for this space, this top-mixing design is rarely used for high speed mixing of fluids, such as fruit juices or milkshake, since the content may spill easily. In addition, although the base allows for an additional heating element, this is often not included since the hot liquid may also easily spill out from the space present.
In the second type of mixers, such as food blenders, the stirring mechanism is located at the base of the housing. The stirring or cutting blades are typically found coupled to the motor at the bottom of the mixing container. The motor coupled to a coupler is fixed to the base, and upon the proper placement of the container, the stirring blade would be securely coupled to the coupler. This base-mixing design allows the high speed mixing of liquids without the danger of spillage, as the container is usually provided with a lid, However, if heating is required, the heating element would have to be provided from the top, for example, in the form of a heating rod attached to the lid of the container. Such a design is undesirable, because electrical wiring has to be wired to the lid, making the manipulation of the lid both dangerous and cumbersome. In addition, a long heating rod which needs to be removed every time the container is filled and emptied results in great inconvenience and safety hazards.